A considerable body of evidence implicates glutamate toxicity as a factor that contributes significantly to motor neuron injury, either as a primary or secondary event, in amyotrophic lateral sclerosis (ALS). Excitotoxicity has been suggested to be important in ALS, mediated by (a) increased glutamate levels that are a consequence of reduced glutamate uptake or (b) increased sensitivity to glutamate (e.g. altered glutamate receptors). Preventing excitotoxicity, for example by increasing the capacity of the cells to transport glutamate from the synaptic cleft, should be beneficial in ALS. We have developed a cell-based assay to screen for molecules that increase glutamate uptake. Using this assay, we recently screened a custom collection of 1,040 FDA-approved drugs and found eight positive hits that consistently augment glutamate uptake in vitro. We now propose to validate these eight effective drugs in a secondary screen in vivo in mice, and to test the hits in a mouse model of ALS as therapeutic candidates for the treatment of the disease. The study will be developed in the following aims: 1) Characterize the effect of the positive hits on the glutamate transport system in vivo. 2) Validate the positive hits in a secondary screen measuring glutamate uptake in synaptosomes from control mice after chronic treatment with the effective drugs. 3) Conduct a trial of the glutamate uptake enhancing compounds in SOD1-G93A transgenic mouse model of ALS. The ultimate goal of this project is to test the drugs effective in the mouse trail in a clinical trial for ALS patients.